Flow control valve for engine cooling water

ABSTRACT

A flow control valve comprises a first valve for controlling a radiator flow amount and a second valve for controlling a bypass flow amount. Pressure adjusting passages are respectively provided for the first and second valves for communicating spaces formed at both sides of the respective valves to equalize fluid pressures at both sides, so that a pressure load in an axial direction to the respective valves can be eliminated. As a result, a driving force of an actuator of the flow control valve for directly or indirectly driving the first and second valves can be reduced.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on Japanese Patent Application No. 2004-205097 filed on Jul. 12, 2004, the disclosures of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a flow control valve to be used in an engine cooling system for a water-cooled engine, in which engine cooling water is circulated to the engine after having been cooled at a radiator. In particular, the present invention relates to a flow control valve for optimizing a temperature of the engine cooling water, by adjusting a flow amount of the engine cooling water flowing through the radiator and a flow amount of the engine cooling water bypassing the radiator, depending on an operational condition of the engine.

BACKGROUND OF THE INVENTION

An engine cooling system for a water-cooled engine is known in the art as a system for cooling an engine mounted in a vehicle having a radiator, in which engine cooling water is circulated into the engine after having been cooled at the radiator. A thermostat is provided in such an engine cooling system, so that the engine cooling water bypasses the radiator by an operation of the thermostat when the temperature of the cooling water is lower than a predetermined value and is circulated back to the engine through a water pump.

In recent years, two opposing requirements for an engine, such as a higher engine output and a lower fuel consumption ratio, have been increased. An engine cooling system, which could meet such requirements for the engine, is accordingly desired. Namely, it is necessary to increase a cooling efficiency at the engine by decreasing the cooling water temperature, and to maintain the temperature at every portion of the engine at such a temperature lower than a durability limit temperature with respect to a thermal load, in order to realize the higher engine output. On the other hand, it is necessary to increase a combustion efficiency at a combustion chamber of the engine, by increasing the cooling water temperature, in order to achieve the lower fuel consumption ratio. As above, such a engine cooling system is required, which could control the cooling water temperature in accordance with various operational conditions of the engine, for example, a high-speed high-load operation of the engine which is a high-speed running of the vehicle with the high engine output, a low-speed high-load operation during the vehicle is running on an up-hilling road, a low-speed low-load operation or a normal operation which is an operation for the low fuel consumption ratio, a re-starting operation of the engine after an engine stop (an engine idling stop operation) for the purpose of a lower harmful emission and the low fuel consumption ratio, and so on.

An engine cooling system for the water-cooled engine has been proposed in the art, in which a flow control valve is provided to make it possible to control the cooling water temperature depending on the various operational conditions of the engine. According to such a cooling system, a flow control valve is provided at an interfluent portion of a cooling water circuit and a bypass circuit, so that a flow amount of the cooling water to the radiator (hereinafter also called as “the radiator flow amount”) and a flow amount of the cooling water bypassing the radiator (hereinafter also called as “the bypass flow amount”) are precisely controlled. The flow control valve can control the cooling water temperature more precisely than the control valve operated by the thermostat, and thereby the lower fuel consumption ratio is achieved.

However, an extremely high fluid pressure is applied by a water pump to a valve body of the flow control valve provided in the engine cooling system, when the valve body is operated by an actuator, independently whether the engine operation is in the high-load operation or in the normal operation. Accordingly, a large operating force or driving torque is necessary for a driving shaft of the actuator to move the valve body. The actuator becomes larger in its size or higher in cost, when it is necessary to provide a reduction device (a gear reduction device) between the driving shaft of the actuator and a moving shaft of the valve body, for reducing a rotational speed of the driving shaft of the actuator to a certain reduction ratio.

In view of the above problem, another flow control valve is proposed, for example, as disclosed in Japanese Patent Publication No. 2003-286843 (which corresponds to U.S. Pat. No. 6,837,193 B2), in which the driving torque required for the actuator is decreased to achieve a small sized actuator. More specifically, a driving load applied to the flow control valve is canceled by a pressure difference between a radiator flow pressure and a bypass flow pressure, to decrease the driving load for the actuator. In the above flow control valve, a first valve body and a first valve seat for controlling the radiator flow amount (of the cooling water flowing through the engine and the radiator and returning to the water pump) and a second valve body and a second valve seat for controlling the bypass flow amount (of the cooling water flowing through the engine, bypassing the radiator, and returning to the water pump) are provided, wherein the first valve body and the second valve body are integrally formed as a single valve body which is then driven by the actuator.

In the above flow control valve, however, the radiator flow pressure and the bypass flow pressure may be largely differed from each other, during the high-load operation of the engine during which only the first valve body is opened, or in a case that a difference between fluid flow resistances appears due to a difference of passage diameters between a radiator side passage and a bypass passage. Then it would become difficult to cancel the driving load applied to the flow control valve the pressure difference between the radiator flow pressure and the bypass flow pressure. As a result, the above flow control valve can not sufficiently achieve the effect for decreasing the driving load to the actuator.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide a flow control valve, in which a load to a driving operation by an actuator is minimized, independently of a closing or opening state of a radiator flow control valve and a bypass flow control valve and independently of fluid pressure of the radiator flow or the bypass flow, by canceling a pressure load to the radiator flow control valve and/or bypass flow control valve during the valve (or valves) is moved in its axial direction.

It is a further object of the present invention to provide a flow control valve, which is smaller in size and which can eliminate a reduction device.

According to a feature of the present invention, a flow control valve comprises a first and a second valve, which are respectively and movably housed in a valve housing, and an actuator for directly or indirectly driving the first and second valves, wherein the first valve controls a radiator flow amount of engine cooling water flowing through a radiator and the second valve controls a bypass flow amount of the engine cooling water bypassing the radiator. The radiator flow amount and the bypass flow amount are independently controlled by the actuator depending on an operational condition of an engine. As a result, a temperature of the engine cooling water can be controlled at a desired value corresponding to the respective operational conditions of the engine.

According to another feature of the present invention, the flow control valve further comprises pressure adjusting passages for the respective first and second valves for communicating with each other spaces formed at both sides of the respective valves, so that the fluid pressure at both sides of the respective valves are equalized. As a result, a pressure load to the first and second valve is cancelled during the valve (or valves) is moved in its axial direction.

According to a further feature of the present invention, the second valve is arranged that an axial direction of the second valve is almost perpendicular to an axial direction of the first valve, so that fluid pressure applied to the second valve does not adversely influence on an axial movement of the first valve, and vice versa.

According to a still further feature of the present invention, a cam face is formed at an outer surface of the first valve, and the second valve is arranged that its axial direction is almost perpendicular to the axial direction of the first valve and a forward end of the second valve is brought into contact with the cam face. As a result, the second valve can be moved in its axial direction in accordance with the axial movement of the first valve, so that a desired characteristic of the bypass flow amount can be obtained by suitably designing a shape of the cam face.

According to a still further feature of the present invention, the flow control valve can be used as a control valve for controlling a heater flow amount, in addition to the radiator flow amount and the bypass flow amount. For the purpose of controlling the heater flow amount of the engine cooling water (hot water) for heating air to be blown into a passenger room of a vehicle, a third valve is movably provided in the flow control valve.

According to the further feature of the present invention, another cam face is likewise formed at the outer surface of the first valve, and the third valve is arranged that its axial direction is almost perpendicular to the axial direction of the first valve and a forward end of the third valve is brought into contact with the cam face. As a result, the third valve can be moved in its axial direction in accordance with the axial movement of the first valve, so that a desired characteristic of the heater flow amount can be obtained by suitably designing a shape of the cam face.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings:

FIG. 1A is a schematic view showing an engine cooling system for a water-cooled engine according to the present invention;

FIG. 1B is a graph showing characteristics of a radiator flow amount and a bypass flow amount with respect to a rotational angle of an actuator;

FIG. 2 is a vertical cross sectional view of a flow control valve, according to a first embodiment of the present invention, showing a starting condition of the valve operation;

FIGS. 3A and 3B are also vertical cross sectional views of the flow control valve, respectively showing a valve condition during a normal operation and a valve condition during a high-load operation;

FIGS. 4A to 4C are cross sectional views, respectively taken along lines IVA-IVA, IVB-IVB, and IVC-IVC in FIG. 2;

FIGS. 5A and 5B are horizontal cross sectional views respectively showing a main portion of a flow control valve according to a second embodiment;

FIGS. 5C and 5D are vertical cross sectional views respectively showing further modifications of the flow control valve according to the second embodiment;

FIG. 6 is a vertical cross sectional view of a flow control valve according to a third embodiment of the present invention;

FIG. 7 is a vertical cross sectional view of a flow control valve according to a fourth embodiment of the present invention;

FIGS. 8A and 8B are respectively a vertical and a horizontal cross sectional views of a flow control valve according to a fifth embodiment and its modification of the present invention;

FIG. 9A is a schematic view showing an engine cooling system for a water-cooled engine according to the fifth embodiment; and

FIG. 9B is a graph showing characteristics of a radiator flow amount, a bypass flow amount and a heater flow amount with respect to a rotational angle of an actuator of the fifth embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

FIGS. 1A to 4C show a first embodiment of the present invention, wherein FIG. 1A shows a schematic view showing an engine cooling system for a water-cooled engine, and FIG. 1B is a graph showing characteristics of a radiator flow amount and a bypass flow amount with respect to a rotational angle of an actuator.

A flow control system according to the present invention comprises an engine cooling system for a water-cooled engine 1 having a cooling water circuit, a flow control valve 2 provided in the cooling water circuit, an electronic control unit (not shown and called hereinafter as ECU) for electronically controlling an opening degree of the flow control valve 2 depending on operational conditions of the engine 1. The flow control valve 2 comprises, as shown in FIG. 2, an actuator 3 to be electronically operated by the ECU, a valve housing 4 which also forms a part of an interfluent portion of the water cooling circuit, a valve body 5 (also referred to as a first spool valve) for controlling a flow amount of the engine cooling water flowing through a radiator 9, and a valve body 6 (also referred to as a second spool valve) for controlling a flow amount of the engine cooling water flowing through a bypass circuit 11 (also referred to as a bypass passage).

The ECU comprises a microcomputer having a well known structure and components, which are CPU for signal processing and calculation, memory devices, such as ROM and RAM, for storing programs and data, an input circuit, an output circuit, a power supply circuit, and so on. Sensor signals from various sensors are inputted into the microcomputer after those signals are processed by A/D converters. Connected to the microcomputer are a crank angle sensor, an acceleration sensor, an intake air flow sensor (an airflow meter, etc.), an intake air temperature sensor, an intake air pressure sensor, a throttle opening sensor, a cooling water temperature sensor on an engine side, a cooling water temperature sensor on a radiator side, a cooling water temperature sensor on a bypass circuit side, a cooling water temperature sensor on a water pump side, and so on. A starter motor drive circuit is connected to the ECU, for controlling a driving current to a starter motor for starting up an engine operation.

When an ignition key is inserted into a key cylinder of a vehicle and turned to a position of “ST”, a starter switch (not shown) is turned on (ST:ON) and a starter relay (not shown) provided in the starter motor drive circuit is turned on. The engine 1 is cranked up to start its operation. When the ignition key is turned back to a position of “IG” and thereby an ignition switch (not shown) is turned on (IG:ON) after the engine 1 has started its operation, the ECU starts its electronic controls to various actuators, such as the flow control valve 2, in accordance with the control programs stored in the memory device. The ECU stops its electronic control when the ignition switch is turned off (IG:OFF).

The engine cooling system comprises the cooling water circuit in which the engine cooling water is circulated to cool the engine 1. The cooling water circuit comprises a radiator cooling circuit in which the cooling water is circulated from and back to a water pump 8 through the engine 1, the radiator 9 and the flow control valve 2. The cooling water circuit further has the bypass circuit in which the cooling water is circulated from and back to the water pump 8 through the engine 1, the bypass passage 11 and the flow control valve 2. As the engine cooling water, an antifreeze liquid having ethylene glycol as a main component, or a long life coolant containing the antifreeze liquid, antirust and the like, is used.

The water pump 8 is arranged adjacent to an output shaft (e.g. a crankshaft) of the engine 1 and integrally provided to an inlet port of the engine 1. The water pump 8 is one of engine accessories driven to rotate by the engine 1 via a transmitting device, such as a belt, and to circulate the cooling water. The water pump 8 can be formed by a pump driven by an electric motor. The engine 1 is mounted in an engine room of the vehicle, and it is the water-cooled engine having a water jacket 12 formed in a cylinder head and a cylinder block of the engine 1, so that the cooling water flows through the engine 1 (through the water jacket). The every portion of the engine 1 is thereby cooled to effectively operate the engine 1.

The radiator 9 is arranged in the engine room and at such a position at which the radiator 9 effectively receives wind during the vehicle running. The radiator 9 comprises an upper tank, a lower tank and a core portion between the upper and lower tanks, wherein the core portion has multiple tubes through which the cooling water flows. In the radiator 9, a heat exchange is performed between the cooling water flowing through the tubes and cooling air passing through between outer surfaces of the multiple tubes, wherein the cooling air is the wind flowing through the radiator during the vehicle running and the wind blown by a cooling fan (not shown). The radiator 9 is, therefore, a heat exchanger for cooling down the cooling water, the water temperature of which is increased as a result of absorbing waste heat of the engine 1 during the cooling water passes through the water jacket 12 of the engine 1.

The radiator cooling circuit comprises passage portions 13 to 16, and the passage portions are liquid-tightly connected to the radiator 9. A downstream side of the passage portion 15 is liquid-tightly connected to an upstream side of the flow control valve 2. The bypass passage 11 is provided, so that the cooling water flowing out of the engine 1 bypasses the radiator 9, wherein the bypass passage 11 branches off from a connecting portion of the passage portions 13 and 14 and is liquid-tightly connected to the upstream side of the flow control valve 2.

A structure of the flow control valve 2 according to the embodiment is explained with reference to FIGS. 2 to 4C. FIG. 2 shows a valve position of the flow control valve at a start of the operation, whereas FIGS. 3A and 3B respectively show the valve positions during the normal operation and at the high-load operation. The flow control valve 2 precisely controls a radiator flow amount of the cooling water flowing in the radiator cooling circuit (13, 14, 9, 15, 2 and 16) as well as a bypass flow amount of the cooling water flowing in the bypass circuit 11, depending on the various operational conditions of the engine. The flow control valve 2 can control the cooling water temperature more precisely than the control valve operated by the thermostat, and thereby the lower fuel consumption ratio is achieved.

The actuator 3 is a driving force generating portion for generating a driving force depending on the engine operation, and comprises a stepping motor for moving the first and second spool valves 5 and 6 in their respective axial directions (in a valve opening or closing direction). A rotor shaft 21 of the actuator 3 is rotationally supported by the valve housing 4. One end of the rotor shaft 21 protrudes into the inside of the valve housing 4, and an oil seal (a shaft seal) is provided between the rotor shaft 21 and the valve housing 4. A male screw portion 23 is formed on an outer periphery of the rotor shaft 21, which is engaged with a female screw portion 57 (FIG. 4C) formed on an inner periphery of the first spool valve 5 movable in its axial direction (in a vertical direction in FIG. 2). A cut-out portion 24 vertically extending (in the axial direction) is formed at the male screw portion 23, as shown in FIG. 4C. Instead of the stepping motor, a brushless motor, a DC motor with brushes, an alternating current motor of a three-phase induction motor can be used for the actuator 3. Further, a solenoid actuator for linearly driving the shaft can be used as the driving force generating portion.

The valve housing 4 is made by an aluminum die-casting process, and is arranged at the interfluent portion at which the passage portions 15 and 16 of the radiator cooling circuit and the bypass passage 11 are jointly connected. A cooling water passage is formed in the valve housing 4. The valve housing 4 has a first cylindrical wall portion 40 a for movingly (reciprocally) supporting the first spool valve 5, a circular pipe joint portion 40 b horizontally extending in the leftward direction in FIG. 2 (FIGS. 3A and 3B) from an outer surface of the first cylindrical wall portion 40 a, a second cylindrical wall portion 40 c horizontally extending in the rightward direction in FIG. 2 (FIGS. 3A and 3B) from the outer surface of the first cylindrical wall portion 40 a and movingly (reciprocally) supporting the second spool valve 6, and a circular pipe joint portion 40 d vertically extending in the upward direction in FIG. 2 (FIGS. 3A and 3B) from an outer surface of the second cylindrical wall portion 40 c. The circular pipe joint portions 40 b and 40 d are respectively connected to the passage portion 16 and the bypass passage 11.

The valve housing 4 further has a circular pipe joint portion 40 e at a lower end of the first cylindrical wall portion 40 a, and a cylindrical valve case 25 is fixed to the circular pipe joint portion 40 e by screws or any other fixing means. An O-ring is provided between the pipe joint portion 40 e and the valve case 25 to prevent leakage of the cooling water. The pipe joint portion 40 e is connected to the radiator 9 through the passage portion 15. A mixing chamber 27 is formed in the inside of the first cylindrical wall portion 40 a, at which the low temperature cooling water cooled down at the radiator 9 and the high temperature cooling water having bypassed the radiator 9 flow into and are mixed together.

A space 31 defined by an upper end surface of the first wall portion 40 a of the valve housing 4 and an upper end surface of the first spool valve 5 is a first volume variable space, the inner volume of which is varied in accordance with the movement of the first spool valve 5 in its axial direction. A space 32 defined by a right-hand end surface of the second cylindrical wall portion 40 c and a right-hand end surface of the second spool valve 6 is a second volume variable space, the inner volume of which is varied in accordance with the movement of the second spool valve 6 in its axial direction. An inner diameter of the pipe joint portion 40 e is made larger than an inner diameter of the first cylindrical wall portion 40 a. A radiator side passage 34 (a first inlet port) is formed in the inside of the pipe joint portion 40 e, so that the cooling water from the radiator 9 flows into the mixing chamber 27.

A bypass side passage 35 (a second inlet port) is formed in the inside of the pipe joint portion 40 d, so that the cooling water from the bypass circuit 11 flows into the mixing chamber 27. A pump side passage 37 (an outlet port) is formed in the inside of the pipe joint portion 40 b, so that the cooling water flows out from the mixing chamber 27 to the water pump 8 through the water pump passage portion 16. The first wall portion (the mixing chamber 27) of the valve housing 4 is respectively connected to the three ports (34, 35 and 37) in a form of a T-shape in the vertical cross section of the valve housing.

The first cylindrical wall portion 40 a of the valve housing 4 has a first cylindrical partitioning portion 40 f for operatively separating the mixing chamber 27 from the radiator side passage 34. A cylindrical inner surface of the first partitioning portion 50 a forms a first sliding surface (a first valve seat), on which a first seal portion (5 a) of the first spool valve 5 reciprocally moves in a sliding manner.

The second cylindrical wall portion 40 c of the valve housing 4 likewise has a second cylindrical partitioning portion 40 g for operatively separating the mixing chamber 27 from the bypass side passage 35. A cylindrical inner surface of the second partitioning portion 40 g forms a second sliding surface (a second valve seat), on which a second seal portion (6 a) of the second spool valve 6 reciprocally moves in a sliding manner.

Multiple first guide portions 4 a are integrally formed in the valve housing 4 at a lower end side of the first cylindrical partitioning portion 40 f, for guiding the first seal portion (5 a) when the first spool valve 5 is downwardly moved. Multiple second guide portions 4 b are likewise integrally formed in the valve housing 4 at a left-hand side of the second cylindrical partitioning portion 40 g, for guiding a protruded small-diameter portion 60 a of the second seal portion (6 a) when the second spool valve 6 is moved in a left-and right-ward direction.

An inside space 41 formed at a lower side of the first cylindrical wall portion 40 a forms a first valve passage 41, which is surrounded by the first guide portions 4 a, the outer surface of the first spool valve 5 and the inner surface of the circular pipe joint portion 40 e. The first valve passage 41 is communicated with the mixing chamber 27; the radiator side passage 34 is communicated with the mixing chamber 27 through the first valve passage 41 when the first spool valve 5 is downwardly moved and opened, as shown in FIG. 3B.

As in the similar manner to the above first valve passage 41, an inside space 42 formed at a left-hand side of the second cylindrical wall portion 40 c forms a second valve passage 42, which is surrounded by multiple second guide portions 4 b, the outer surface of the second spool valve 6 and the inner surface of the second wall portion 40 c. The second valve passage 42 is communicated with the mixing chamber 27; the bypass side passage 35 is communicated with the mixing chamber 27 through the second valve passage 42 when the second spool valve 6 is moved in the rightward direction and opened, as shown in FIG. 3A.

The first spool valve 5 is urged by a return spring 44 in a valve opening direction (a downward direction in FIG. 2), to prevent overheat of the engine at a system failure. The first spool valve 5 is prevented from rotating by a stopper pin 51 fixed to the valve housing 4, so that the first spool valve 5 can be reciprocally moved in the axial direction (in the upward and downward direction) when the rotor shaft 21 is rotated by the actuator 3. When the first spool valve 5 is upwardly or downwardly moved upon receiving the driving force from the rotor shaft 21, an opening degree of the first valve passage 41 is varied to control the radiator flow amount. As above, the first spool valve 5 functions as a control valve for the radiator flow amount.

The first spool valve 5 comprises a pair of rand portions 5 a and 5 b (each of which has a disc portion, an outer periphery and a sealing portion), a cylindrical portion 5 c connecting the rand portions 5 a and 5 b with each other, and a side wall portion 5 d which is formed into an arc-shape and between the outer peripheries of the two rand portions 5 a and 5 b. The side wall portion 5 d is formed so that it faces to the second spool valve 6. A pair of ring seal grooves is formed at the outer peripheries of the rand portions 5 a and 5 b, into which ring seals 47 a and 47 b are inserted. The ring seal 47 b is liquid-tightly in contact with the inner surface of the first cylindrical wall portion 40 a, for separating the first volume variable space 31 from the mixing chamber 27.

The other ring seal 47 a is likewise liquid-tightly in contact with the inner surface of the first partitioning portion 40 f, for operatively separating the radiator side passage 34 (the first valve passage 41) from the mixing chamber 27. Accordingly, a desired radiator flow amount, as shown in FIG. 1B, with respect to the rotational angle of the actuator 3 can be obtained, when the dimension of the pair of the rand portions 5 a and 5 b as well as the first sliding surface (the longitudinal dimension thereof) are suitably selected.

The cylindrical portion 5 c of the first spool valve 5 has the female screw portion 57 which is formed at its inner periphery and engaged with the male screw portion 23 of the rotor shaft 21. A space 5 e is formed between the two rand portions 5 a and 5 b at the outer periphery of the cylindrical portion 5 c, wherein the space 5 e forms wholly or partly the mixing chamber 27. As above, the first spool valve 5 is moved upwardly or downwardly in response to the rotation of the rotor shaft 21, wherein the male screw portion 23 and the female screw portion 57 form a driving direction changing device. A thick wall portion is provided at the side wall portion 5 d of the first spool valve 5, wherein an insertion hole is formed so that one end of the stopper pin 51 is inserted. A profile 52 is formed at an outer surface of the thick wall portion (5 d), so that the second spool valve 6 is moved in conjunction with the first spool valve 5. The profile 52 comprises a concave and a convex portion, which are so formed to obtain the desired bypass flow amount, as shown in FIG. 1B, with respect to the rotational angle of the actuator 3.

The profile 52 is formed as a cam face for driving the second spool valve 6 in its axial direction (i.e. in a direction perpendicular to an axial direction of the first spool valve 5). The cam face (52) comprises a first and a second flat surface portions 52 a and 52 d (concave portions) extending in parallel to the axial direction of the first spool valve 5, a first and a second inclined surface portions 52 b and 52 c protruding outwardly from the first and second flat surface portions 52 a and 52 d and each having an inclined angle with respect to the axial direction of the first spool valve 5. The first and second inclined surface portions 52 b and 52 c form a convex portion, and the inclined angle of the first inclined surface portion 52 b (with which a ball 55 of the second spool valve 6 is in contact, when the first spool valve 5 is positioned at its starting position, as shown in FIG. 2) is made larger than that of the inclined surface portion 52 c (with which the ball 55 is brought into contact, when the first spool valve 5 is moved downwardly to its normal operation or high load operation position, as shown in FIGS. 3A and 3B).

A first pressure adjusting passage 61 is formed between the inner surface (the female screw portion 57) of the cylindrical portion 5 c of the first spool valve 5 and the cut-out portion 24 of the rotor shaft 21, as shown in FIG. 4C, for communicating with each other the spaces formed at outer sides of the pair of the rand portions 5 a and 5 b. More specifically, the first pressure adjusting passage 61 communicates the first volume variable space 31 with the radiator side passage 34 (i.e. the first valve passage 41) for equalizing the fluid pressures in the both spaces.

The second spool valve 6 is biased by a set spring 45 toward the first spool valve 5, so that the second spool valve 6 is brought into contact with the profile 52 of the first spool valve 5 via the ball 55. The second spool valve 6 is moved in its axial direction (in a direction perpendicular to the axial direction of the first spool valve) in accordance with the movement of the first spool valve 5. When the first spool valve 5 is downwardly moved, from the position of FIG. 2 to the position of FIG. 3A, the second spool valve 6 is moved in its right-hand direction to change the opening degree of the second valve passage 42, so that the bypass flow amount is controlled. The second spool valve 6 operates as a bypass flow control valve, as above.

The second spool valve 6 comprises a pair of rand portions (i.e. the second seal portions) 6 a and 6 b which are supported by the second sliding surface in the sliding manner, and a cylindrical portion 6 c connecting the rand portions 6 a and 6 b with each other. The rand portion 6 b of the second spool valve 6 liquid-tightly separates the second volume variable space 32 from the bypass side passage 35. The second volume variable space 32 is liquid-tightly closed by a plug member 58.

The other rand portion 6 a of the second spool valve 6 operatively and liquid-tightly separates the bypass side passage 35 from the second valve passage 42 (and thereby the mixing chamber 27). The protruded small-diameter portion 60 a is formed at the other rand portion 6 a, protruding outwardly (in a leftward direction) from the rand portion 6 a and in the axial direction of the second spool valve 6. A recess portion 64 is formed at a forward end of the protruded small-diameter portion 60 a, for holding the ball 55.

Accordingly, a desired bypass flow amount, as shown in FIG. 1B, with respect to the rotational angle of the actuator 3 can be obtained, when the dimensions of the pair of the rand portions 6 a and 6 b, the second sliding surface (the longitudinal dimension thereof), and the profile 52 are suitably selected.

A space 6 e is formed between the two rand portions 6 a and 6 b and at the outer periphery of the cylindrical portion 6 c, wherein the space 6 e forms wholly or partly the bypass side passage 35. A second pressure adjusting passage 62 is formed in the cylindrical portion 6 c, as shown in FIGS. 2 and 4A, for communicating with each other the spaces formed at outer sides of the pair of the rand portions 6 a and 6 b. More specifically, the second pressure adjusting passage 62 communicates the second volume variable space 32 with the mixing chamber 27 through the second valve passage 42 for equalizing the fluid pressures in the both spaces. According to the present embodiment, the protruded small-diameter portion 60 a is formed at the rand portion 6 a and the recess portion 64 is formed at its forward end, and therefore the second pressure adjusting passage 62 is formed into an L-shaped passage, as shown in FIG. 2.

An operation of the above engine cooling system is explained with reference to FIGS. 1 to 4.

The actuator 3 of the flow control valve 2 is controlled by the ECU to change the opening degrees of the first and second spool valves 5 and 6 depending on the operational condition of the water cooled engine 1, as shown in FIG. 1B. The first spool valve 5 is moved in its axial direction (in the valve opening or closing direction) upon directly receiving the driving force from the rotor shaft 21, wherein the rotational movement of the rotor shaft 21 is converted into the linear movement by the screw portion 23, so that the opening degree of the first valve passage 41 is increased or decreased. As a result, the radiator flow amount of the engine cooling water flowing in the radiator cooling circuit can be controlled in accordance with the engine operational condition.

The second spool valve 6 is moved in its axial direction (in the valve opening or closing direction) upon indirectly receiving the driving force from the rotor shaft 21 through the first spool valve 5 and the ball 55 being in contact with the profile 52 formed in the first spool valve 5, so that the opening degree of the second valve passage 42 is likewise increased or decreased. As a result, the bypass flow amount of the engine cooling water flowing in the bypass circuit can be controlled in accordance with the engine operational condition. As above, the radiator flow amount as well as the bypass flow amount can be precisely controlled in accordance with the engine operational condition, so that the temperature of the engine cooling water flowing through the water jacket 12 can be controlled at such a temperature which is most suitable for the respective engine operation conditions.

The first and second spool valves 5 and 6 are controlled in the following manner, in accordance with the engine operational conditions. At a starting period of the engine 1, the actuator 3 is operated to move the first and second spool valves 5 and 6 to the positions shown in FIG. 2. In this position, the rand portion 5 b of the first spool valve 5 is in the sliding contact with the inner surface of the valve housing 4, whereas the other rand portion 5 a is in the sliding contact with first sliding surface (i.e. the first valve seat 40 f). Accordingly, the first valve passage 41 is separated from the mixing chamber 27 and the pump side passage 37.

As in the same manner to the first spool valve 5, the rand portion 6 b of the second spool valve 6 is in the sliding contact with the inner surface of the valve housing 4 (the second sliding surface at the right-hand side), whereas the other rand portion 6 a is in the sliding contact with the second sliding surface (the second valve seat 40 g). Accordingly, the bypass side passage 35 is separated from the second valve passage 42 and the mixing chamber 27.

As above, the first and second spool valves 5 and 6 are closed during the period for the engine starting operation, as shown in FIG. 1B, so that the radiator flow amount of the engine cooling water circulating in the radiator cooling circuit as well as the bypass flow amount of the engine cooling water circulating in the bypass circuit are both zero.

When the engine is operated in its normal operation but the temperature of the engine cooling water detected by the temperature sensor on the engine side is below a predetermined value, for example 60 to 78° C., the first spool valve 5 is downwardly moved from its starting position of FIG. 2, to a position shown in FIG. 3A. In this valve position, the rand portion 5 a of the first spool valve 5 is still in the sliding contact with the first valve seat 40 f, so that the separation between the first valve passage 41 and the mixing chamber 27 (and the pump side passage 37) is maintained.

On the other hand, the ball 55 of the second spool valve 6 is lifted up (moved in the right-hand direction) by the convex portion of the profile 52 formed in the thick wall portion of the first spool valve 5, as shown in FIG. 3A, and thereby the rand portion 6 a of the second spool valve 6 is separated from the second sliding surface (the second valve seat 40 g). The bypass side passage 35 is communicated from the second valve passage 42 and the mixing chamber 27.

As a result, since the first spool valve 5 is kept closed whereas the second spool valve 6 is opened, the radiator flow amount of the engine cooling water circulating in the radiator cooling circuit is still zero, whereas the bypass flow amount of the engine cooling water circulating in the bypass circuit is controlled to become such an amount corresponding to the opening degree of the second spool valve 6 (i.e. the amount of the movement of the second spool valve 6).

When the second spool valve 6 is opened as above, the engine cooling water pumped out from the water pump 8 circulates through the water jacket 12 of the engine 1, the passage portion 13, the bypass passage 11, the bypass side passage 35 of the flow control valve 2, the second valve passage 42, the mixing chamber 27, the pump side passage 37 and the passage portion 16. During this operation, the temperature of the engine cooling water is gradually increased, due to the engine cooling water flowing through the water jacket 12 of the engine 1, to reach the predetermined value.

When the temperature of the engine cooling water detected by the temperature sensor on the engine side becomes higher than the predetermined value, for example 60 to 78° C., during the normal operation of the engine, the first spool valve 5 is further downwardly moved from its first normal position of FIG. 3A, toward a position shown in FIG. 3B. In this valve position (before reaching the position of FIG. 3B), the rand portion 5 a of the first spool valve 5 is separated from the first valve seat 40 f, so that the first valve passage 41 is brought into communication with the mixing chamber 27 and the pump side passage 37.

The contact between the ball 55 and the profile 52 of the first spool valve 5 is changed from the contact with the first inclined surface 52 b to the contact with the second inclined surface 52 c, and the second spool valve 6 is gradually moved in the leftward direction (in the valve closing direction) by the biasing force of the set spring 45 in proportion to the downward movement of the first spool valve 5.

As above, the first spool valve 5 starts its opening operation whereas the second spool valve 6 is moved to its closing position, when the temperature of the engine cooling water detected by the temperature sensor on the engine side becomes higher than the predetermined value, for example 60 to 78° C., during the normal operation of the engine. Accordingly, as shown in FIG. 1B, the radiator flow amount of the engine cooling water circulating in the radiator cooling circuit is controlled to be such an amount corresponding to a stroke of the downward movement (i.e. the opening degree) of the first spool valve 5, whereas the bypass flow amount of the engine cooling water circulating in the bypass circuit is controlled to be such an amount corresponding to a stroke of the leftward movement (i.e. the opening degree) of the second spool valve 6.

When the first spool valve 5 is opened as above, the engine cooling water pumped out from the water pump 8 circulates through the water jacket 12 of the engine 1, the passage portion 13, the radiator passage portion 14, the radiator 9, the radiator passage portion 15, the radiator side passage 34 of the flow control valve 2, the first valve passage 41, the mixing chamber 27, the pump side passage 37 and the passage portion 16. On the other hand, since the second spool valve 6 is still in its opened state, the engine cooling water pumped out from the water pump 8 circulates through the water jacket 12 of the engine 1, the passage portion 13, the bypass passage 11, the bypass side passage 35 of the flow control valve 2, the second valve passage 42, the mixing chamber 27, the pump side passage 37 and the passage portion 16. Due to the above operation, the temperature of the engine cooling water flowing through the water jacket 12 of the engine 1 is maintained at the predetermined value.

When the engine 1 is operated with high load, the first spool valve 5 is further downwardly moved from its second normal position, to the position shown in FIG. 3B. In this valve position (FIG. 3B), the rand portion 5 a of the first spool valve 5 is further separated from the first valve seat 40 f, so that the opening degree of the first valve passage 41 is made larger than that during the normal operation, whereas the ball 55 is brought into contact with the flat surface portion 52 d of the profile 52 of the first spool valve 5 and the rand portion 6 a of the second spool valve 6 is thereby brought into the sliding contact with the second sliding surface (40 g) to close the second valve passage 42. The bypass side passage 35 is thereby separated from the second valve passage 42 and the mixing chamber 27. As a result, since the first spool valve 5 is kept opened whereas the second spool valve 6 is closed, as shown in FIG. 1B, the radiator flow amount of the engine cooling water circulating in the radiator cooling circuit is continuously controlled to be the amount corresponding to the stroke of the downward movement (i.e. the opening degree) of the first spool valve 5, whereas the bypass flow amount of the engine cooling water circulating in the bypass circuit becomes zero.

Since the first spool valve 5 is kept opened as above, the engine cooling water pumped out from the water pump 8 circulates through the water jacket 12 of the engine 1, the passage portion 13, the radiator passage portion 14, the radiator 9, the radiator passage portion 15, the radiator side passage 34 of the flow control valve 2, the first valve passage 41, the mixing chamber 27, the pump side passage 37 and the passage portion 16. In this operation, since a larger amount of the engine cooling water flowing through the water jacket 12 of the engine 1 is cooled down at the radiator, the temperature of the engine cooling water can be maintained at the predetermined value. As indicated in FIG. 1B, it is not always necessary to completely close the second valve passage 42. Instead, the opening degree of the second valve passage 42 can be reduced to a smaller amount than that during the normal operation.

According to the first embodiment, as described above, since the first volume variable space 31 is communicated with the space formed at the opposite side of the first spool valve 5 (i.e. the first valve passage 41 and the radiator side passage 34) through the first pressure adjusting passage 61, the fluid pressures at both of the longitudinal sides of the first spool valve 5 is equalized (P1=P2). As a result, the pressure load for the movement of the first spool valve 5 in its axial direction (in the upward-downward direction in FIG. 2) can be cancelled.

As in the same manner to the first spool valve 5, since the second volume variable space 32 is communicated with the space formed at the opposite side of the second spool valve 6 (i.e. the second valve passage 42 and the mixing chamber 27) through the second pressure adjusting passage 62, the fluid pressures at both of the longitudinal sides of the second spool valve 6 is equalized (P3=P4). As a result, the pressure load for the movement of the second spool valve 6 in its axial direction (in the leftward-rightward direction in FIG. 2) can be cancelled.

As above, the driving load for the actuator 3 of the flow control valve 2 can be minimized, independently of the valve opening or valve closing positions of the first and second spool valves 5 and 6, and further independently of fluid pressure in the radiator cooling circuit (more specifically, the fluid pressure in the radiator side passage 34) or the fluid pressure in the bypass circuit (more specifically, the fluid pressure in the bypass side passage 35). The flow control valve 2 can be therefore made in a smaller size, and made in a lower cost since a reduction device for reducing a rotational speed of the actuator by a predetermined reduction ratio can be eliminated. Since the flow amount characteristics shown in FIG. 1B can be freely changed by changing the shape of the profile 52, the main components of the flow control valve 2 can be commonly used for various types of the flow control valves, independently of different requirements for the different cooling systems or different vehicle models. And therefore, the development cost can be also reduced.

Second Embodiment

A second embodiment will be explained with reference to FIGS. 5A to 5D, wherein the second embodiment differs from the first embodiment in that the first pressure adjusting passage 61 is modified, instead of providing the cut-out portion 24 at the rotor shaft 21.

FIG. 5A shows a cross sectional view of the cylindrical portion 5 c of the first spool valve 5. A part of the cylindrical portion 5 c is extended in a radial direction to form the first pressure adjusting passage 61.

FIG. 5B also shows a cross sectional view of the cylindrical portion 5 c of the first spool valve 5. Three parts of the cylindrical portion 5 c are extended in radial directions to form multiple pressure adjusting passages 61.

FIG. 5C shows a vertical cross sectional view of the flow control valve 2, wherein the first pressure adjusting passage 61 is formed in the side wall portion 5 d of the first spool valve 5.

FIG. 5D also shows a vertical cross sectional view of the flow control valve 2, wherein a connecting pipe portion 69 is provided between the rand portions 5 a and 5 b and the first pressure adjusting passage 61 is formed in the connecting pipe portion 69.

In the above modifications, the first pressure adjusting passage 61 is formed in the first spool valve 5. However, although not shown in the drawings, the first pressure adjusting passage can be formed in the valve housing 4.

According to the above second embodiment, the cross sectional area of the first pressure adjusting passage 61 can be freely designed, more specifically the cross sectional area can be made larger than that of the first embodiment, so that the pressure equalization between the first volume variable space 31 and the first valve passage 41 (i.e. radiator side passage 34) can be more smoothly performed.

Third Embodiment

A third embodiment will be explained with reference to FIG. 6.

The forward end 70 of the protruded small-diameter portion of the second spool valve 6 is formed into a semispherical shape, so that the ball 55 of the first embodiment can be eliminated. According to the third embodiment, the number of parts as well as number of assembling processes for the flow control valve can be reduced to realize a cost down.

Fourth Embodiment

A fourth embodiment will be explained with reference to FIG. 7.

A blade portion 71 is formed at the rand portion 5 a of the first spool valve 5, for rectifying the fluid flow in the radiator side passage 34 and the first valve passage 41 to reduce fluid resistance for the engine cooling water flowing from the radiator 9 into the flow control valve 2. As a result, the flow amount can be increased at the full open state of the first spool valve 5, to maximally bring out the cooling effect of the radiator 9.

Fifth Embodiment

A fifth embodiment will be explained with reference to FIGS. 8A to 9B, wherein FIG. 8A is a vertical cross sectional view of the flow control valve, FIG. 8B is a cross sectional view of a modified flow control valve, FIG. 9A is a schematic view showing an engine cooling system, and FIG. 9B is a graph showing characteristics of a radiator flow amount, a bypass flow amount and a heater flow amount with respect to a rotational angle of an actuator. The same reference numerals to the first embodiment are those parts which are identical or similar to the first embodiment.

The engine cooling system shown in FIG. 9A comprises three different flow circuits; a radiator cooling circuit in which the engine cooling water flows from the water pump 8 through the engine 1, the radiator 9, the flow control valve 2 and back to the water pump 8; a bypass circuit in which the engine cooling water flows from the water pump 8 through the engine 1, the bypass passage 11, the flow control valve 2 and back to the water pump 8; and a heater circuit in which the engine cooling water (hot water) flows from the water pump 8 through the engine 1, a hot water type heater 10 for an air conditioning system, the flow control valve 2 and back to the water pump 8.

The hot water type heater 10 is provided in an air duct of a vehicle air conditioning device for air-conditioning a passenger room of a vehicle. The heater 10 comprises a heater core having a pair of tanks and multiple tubes connected between the tanks, so that the engine cooling water (the hot water) flows from one of the tanks to the other tank through the tubes. When air passes by the heater 10, heat is exchanged between the hot water flowing through the tubes and the air flowing around outer surfaces of the tubes, so that the air cooled down by an evaporator (not shown) is re-heated by the heater 10. At the same time, the engine cooling water (hot water) heated by the waste heat of the engine 1 can be cooled down by the heater 10. The heater 10 is connected to the engine 1 through a heater passage 17 and to the flow control valve through another heater passage 18, which is liquid-tightly connected to the flow control valve 2.

The flow control valve 2 comprises a third spool valve 7, in addition to the first and second spool valves 5 and 6 which are basically identical to those shown in FIG. 2. The third spool valve 7 is also similar in its structure to the second spool valve 6 and is biased by a set spring 46 toward the first spool valve 5, so that the third spool valve 7 is brought into contact with a profile 53 of the first spool valve 5 via a ball 56. The third spool valve 7 is moved in its axial direction (in a direction perpendicular to the axial direction of the first spool valve) in accordance with the movement of the first spool valve 5. When the first spool valve 5 is downwardly moved, the third spool valve 7 is moved in its right-hand direction to change an opening degree of a third valve passage 43, so that the heater flow amount is controlled. The third spool valve 7 operates as a heater flow control valve, as above. When the third spool valve 7 is opened, a heater side passage 36 is communicated with the third valve passage 43, the mixing chamber 27 and the pump side passage 37.

The third spool valve 7 comprises a pair of rand portions (i.e. third seal portions) 7 a and 7 b which are supported by a third sliding surface in the sliding manner, and a cylindrical portion 7 c connecting the rand portions 7 a and 7 b with each other. The rand portion 7 b of the third spool valve 7 liquid-tightly separates a third volume variable space 33 from the heater side passage 36. The third volume variable space 33 is liquid-tightly closed by a plug member 59. A guide portion 4 c is integrally formed in the valve housing 4, for guiding the third spool valve 7.

The other rand portion 7 a of the third spool valve 7 operatively and liquid-tightly separates the heater side passage 36 from the third valve passage 43 (and thereby the mixing chamber 27). The protruded small-diameter portion 70 a is formed at the other rand portion 7 a, protruding outwardly (in a leftward direction) from the rand portion 7 a and in the axial direction of the third spool valve 7. A recess portion 65 is formed at a forward end of the protruded small-diameter portion 70 a, for holding the ball 56.

Accordingly, a desired heater flow amount, as shown in FIG. 9B, with respect to the rotational angle of the actuator 3 can be obtained, when the dimensions of the pair of the rand portions 7 a and 7 b, the third sliding surface (the longitudinal dimension thereof), and the profile 53 are suitably selected.

A space 7 e is formed between the two rand portions 7 a and 7 b and at the outer periphery of the cylindrical portion 7 c, wherein the space 7 e forms wholly or partly the heater side passage 36. A third pressure adjusting passage 63 is formed in the cylindrical portion 7 c, as shown in FIGS. 8A and 8B, for communicating with each other the spaces formed at outer sides of the pair of the rand portions 7 a and 7 b. More specifically, the third pressure adjusting passage 63 communicates the third volume variable space 33 with the mixing chamber 27 through the third valve passage 43 for equalizing the fluid pressures in the both spaces. According to the present embodiment, the protruded small-diameter portion 70 a is formed at the rand portion 7 a and the recess portion 65 is formed at its forward end, and therefore the third pressure adjusting passage 63 is formed into an L-shaped passage, as shown in FIG. 8A. The third spool valve 7 is formed in the valve housing 4 in the same vertical line to the second spool valve 6, as shown in FIG. 8A. However, it can be formed in the same horizontal line to the second spool valve 6, as shown in FIG. 8B, wherein the third spool valve 7 is displaced from the second spool valve 6 by a certain angle. As above, in the case that a further spool valve is formed in the flow control valve, the further spool valve can be formed in the similar manner to the third spool valve 7.

According to the above fifth embodiment, the heater flow amount can be controlled in addition to the radiator flow amount and the bypass flow amount, without largely increasing the driving load to the actuator 3. The flow control valve 2 can be therefore made in a small size, compared with a case in which a heater valve for controlling the heater flow amount is independently provided.

Furthermore, since the heater flow amount can be controlled independently from the control for the radiator flow or the bypass flow, the heater passages 17 and 18 can be communicated by the flow control valve 2 before the radiator cooling circuit and the bypass circuit are opened, when the temperature of the heater 10 is to be rapidly and preferentially increased, as shown in FIG. 9B, during a period of a heater preferential operation. Accordingly, the waste heat from the engine can be intensively supplied to the heater 10 for quickly warming the passenger room of the vehicle.

Furthermore, the multiple spool valves 6 and 7 can be arranged in the valve housing 4 in any manner as desired, it becomes possible to design the flow control valve realizing the best arrangement to the cooling system. 

1. A flow control valve of engine cooling water for a vehicle comprising: a valve housing having a first inlet port to be connected to a radiator, a second inlet port to be connected to a bypass passage and an outlet port to be connected to a water pump, the valve housing further having a first valve passage forming a part of a radiator cooling circuit in which the engine cooling water is circulated from the an engine to the water pump through the radiator, the valve housing further having a second valve passage forming a part of a bypass circuit in which the engine cooling water is circulated from the engine to the water pump through the bypass passage bypassing the radiator; an actuator for generating a driving force in accordance with an operational condition of the engine; a first valve movably housed in the valve housing and moved in its axial direction upon operatively receiving the driving force from the actuator, so that an opening degree of the first valve passage is controlled; a second valve movably housed in the valve housing and moved in its axial direction upon operatively receiving the driving force from the actuator, so that an opening degree of the second valve passage is controlled; and a pressure adjusting passage for equalizing fluid pressures at both axial sides of at least one of the first and the second valves.
 2. A flow control valve according to claim 1, wherein the pressure adjusting passage is formed in the first valve, extending in the axial direction to communicate spaces respectively formed at the both axial sides of the first valve with each other.
 3. A flow control valve according to claim 1, wherein the pressure adjusting passage is formed in the second valve, extending in the axial direction to communicate spaces respectively formed at the both axial sides of the second valve with each other.
 4. A flow control valve according to claim 1, wherein the actuator has a rotor shaft rotating at an axis which is coaxial with a center axis of the first valve, and the axial direction of the second valve is almost perpendicular to the axial direction of the rotor shaft.
 5. A flow control valve according to claim 4, wherein the first valve has a profile for driving the second valve in its axial direction, so that a desired bypass flow amount with respect to a rotational angle of the rotor shaft is obtained, and the second valve is biased toward the profile by a biasing means.
 6. A flow control valve according to claim 1, wherein the valve housing further comprises: a mixing chamber for mixing the engine cooling water of a low temperature from the radiator with the engine cooling water of a high temperature bypassing the radiator; a radiator side passage for flowing the engine cooling water from the radiator into the mixing chamber; a bypass side passage for flowing the engine cooling water from the bypass passage into the mixing chamber; and a pump side passage for flowing out the engine cooling water from the mixing chamber to the water pump.
 7. A flow control valve according to claim 1, wherein the valve housing has further a third valve passage forming a part of a heater circuit in which the engine cooling water is circulated from the engine to the water pump through a heater.
 8. A flow control valve according to claim 7, further comprising: a third valve movably housed in the valve housing and moved in its axial direction upon operatively receiving the driving force from the actuator, so that an opening degree of the third valve passage is controlled; and another pressure adjusting passage for equalizing fluid pressures at both axial sides of the valve.
 9. A flow control valve according to claim 8, wherein the other pressure adjusting passage is formed in the third valve, extending in the axial direction to communicate spaces respectively formed at the both axial sides of the third valve with each other.
 10. A flow control valve according to claim 8, wherein the actuator has a rotor shaft rotating at an axis which is coaxial with a center axis of the first valve, and the axial direction of the third valve is almost perpendicular to the axial direction of the rotor shaft.
 11. A flow control valve according to claim 10, wherein the first valve has a profile for driving the third valve in its axial direction, so that a desired heater flow amount with respect to a rotational angle of the rotor shaft is obtained, and the third valve is biased toward the profile by a biasing means.
 12. A flow control valve according to claim 7, wherein the valve housing further comprises: a mixing chamber for mixing the low temperature engine cooling water radiated at the heater, the engine cooling water of a low temperature from the radiator and the engine cooling water of a high temperature bypassing the radiator with one another; a heater side passage for flowing the engine cooling water from the heater into the mixing chamber; a radiator side passage for flowing the engine cooling water from the radiator into the mixing chamber; a bypass side passage for flowing the engine cooling water from the bypass passage into the mixing chamber; and a pump side passage for flowing out the engine cooling water from the mixing chamber to the water pump. 